The present invention relates to an optical fiber-lens array, and more specifically to a connecting structure between a gradient index rod lens and an optical fiber.
Hitherto, optical information transmission has been performed by the steps of converging outgoing light from one of optical fibers by means of a lens to make collimated lights, propagating the collimated lights, converging said collimated lights by means of another lens and launching them into the other optical fiber, or by the steps of converging outgoing light from the optical fiber by means of a lens and then optically combining them into an optical component. Such an optical system may construct a variety of optical modules by placing a light element such as a laser diode or photodiode on the side of light convergence, or by interposing various optical components such as a filter, an optical isolator, an optical switch, or an optical modulator between both lenses.
Though the lens used here is a convex lens, an optical fiber-lens array may be constructed using a gradient index rod lens. The rod lens of gradient index type has a characteristic in which the refraction index changes gradually in the direction of the radius from the axis thereof, so that incoming light may be converted into collimated lights or converged and launched by defining the length of the lens or the distance between the lens and the optical fiber according to the wavelength. In the optical fiber-lens array employing a gradient index rod lens as described above, it is required to coincide the optical axis of the gradient index rod lens with the optical axis of the optical fiber with high accuracy to reduce the coupling loss and thus the connecting structure as described below has been employed.
In other words, as shown in FIG. 9, such a connecting structure is employed that the gradient index rod lens 1 is fitted into the sleeve 2 through one of the ends thereof and an optical fiber 3 fitted with a capillary tube 4 thereon is fitted into the sleeve 2 from the other end thereof and the end surface of the gradient index rod lens 1 is abutted to the end surface of the optical fiber 3 so that their optical axes L coincide. This connecting structure is called a single core collimator, which is used by being accommodated in a V-shaped groove 6 formed on the substrate 5 when building an optical module together with other optical components.
As shown in FIG. 10, another connecting structure is employed, in which a V-shaped groove for rod lens 6a for accommodating a gradient index rod lens 1 is formed from one of the ends of the substrate 5 (left end in the figure) to the center thereof, and a V-shaped groove for optical fiber 6b is formed from the other end to the end of the V-shaped groove for rod lens 6a, and a gradient index rod lens 1 and an optical fiber 3 are accommodated in the corresponding V-shaped grooves 6a and 6b respectively. The widths of the opening and the tilt angles of the V-shaped groove 6a for rod lens and the V-shaped groove 6b for optical fiber are, as shown in the cross sectional view taken along the line Bxe2x80x94B of the same figure, determined respectively so that both of the optical axes L coincide with the gradient index rod lens 1 and the optical fiber 3 accommodated.
However, the connecting structure as shown in FIG. 9 requires troublesome and complex operations such as fitting the gradient index rod lens 1 into the sleeve 2, fitting a capillary tube 4 on the optical fiber 3 and then fitting it into the sleeve 2 another time, to produce a single-core collimator. In addition, it requires accessories such as a sleeve 2 and a capillary tube 4, and there may be cases in which the optical axes L do not coincide depending on the accuracy of the capillary tube 4 or the state of assembly of the optical fiber 3 and the capillary tube 4, whereby adjustment of the optical axes L is inevitable. Moreover, since an optical fiber-lens array comprising a plurality of gradient index rod lenses 1 and optical fibers 3 are used in many cases, a plurality of assemblies, each having an optical fiber and a lens of a single common axis as shown in FIGS. 9 and 10, and a new substrate must be prepared, and even another assembling operation are required additionally to accommodate such circumustances.
In the connecting structure as shown in FIG. 10, two V-shaped grooves 6a, 6b, being different in width or depth of the opening, or even in tilt angle, have to be formed on the same substrate with high accuracy. However, in the collimators of this type, since it is common to use silicon as a material for the substrate and that the V-shaped groove is formed by etching by means of lithography technique, it is difficult to form at once with the two grooves of different shape abutted against with respect to each other, and thus the process accuracy is difficult to realize. In the case of the collimator, since the displacement of the optical axes between the gradient index rod lens 1 and the optical fiber 3 must be at most about 2 xcexcm in order to suppress the amount of attenuation to generally 1 dB or less, the respective V-shaped grooves 6a, 6b is required to be processed with a significantly high degree of accuracy even on individual basis, and thus still higher degree of accuracy is required to process the two V-shaped grooves 6a and 6b into a precisely abutted configuration.
With such a circumstances in view, it is an object of the present invention to provide a connecting structure in which the alignment of the optical axes between the gradient index rod lens and an optical fiber can be realized with high accuracy and easily in the optical fiber-lens array.
In order to achieve the object described above, the present invention provides an optical fiber-lens array comprising a first substrate having a gradient index rod lens accommodated in V-shaped grooves for rod lenses formed in parallel at prescribed pitches, and a second substrate having optical fibers accommodated in V-shaped grooves for optical fibers formed at the same array pitches as the V-shaped grooves for rod lenses. In the array, the first substrate and the second substrate are connected by guide pins placed on the common positioning guide grooves formed on the first substrate and the second substrate with the respective end surfaces of the gradient index rod lenses and the respective end surfaces of the corresponding optical fibers faced toward each other.
In order to achieve the same object, the present invention provides an optical fiber-lens array comprising a first substrate including gradient index rod lenses inserted into insertion holes for rod lenses formed therethrough in parallel at prescribed pitches and a second substrate including optical fibers inserted into insertion holes for optical fibers formed therethrough in parallel at the same array pitches as the insertion hole for rod lens. In the array, the first substrate and the second substrate are connected by guide pins so that the positioning holes formed through the first substrate and the second substrate are in communication with respect to each other with the end surfaces of the respective gradient index lenses and the end surfaces of corresponding optical fibers faced toward each other.
The present disclosure relates to the subject matter contained in Japanese patent application No. 2000-55768 (filed on Mar. 1, 2000), which is expressly incorporated herein by reference in its entirety.